The present invention relates a method of spooling a marine pipeline.
Corrosion resistance pipelines for the marine or otherwise underwater transportation or conveying of corrosive fluids such as gas or crude oil can be provided by pipes having an internal metallic liner. A double-walled or bi-metallic pipe is generally composed of two metallic layers. The outer layer is for resisting hydrostatic pressure, and/or internal pressure depending on the water depth, whilst the internal layer prevents damage to the outer layer from the chemical composition of the fluid being conveyed. The inner layer is sometimes also termed a “liner”. As one of its main purposes is to protect the outer layer from corrosion, commonly a corrosion resistant alloy (CRA) is chosen for the liner.
One form of bi-metallic pipe is a single “clad” pipe having an internal CRA layer metallurgically bonded to the outer layer, which could be formed from a carbon steel base metal.
A second form of bi-metallic pipe can be termed a ‘lined’ pipe, where a CRA liner is fixed to the outer layer such as carbon steel without metallurgical bonding. An economic method of forming a lined pipe uses hydraulic expansion, where the CRA liner is inserted into the outer layer, and then both parts are expanded. During the expansion, the outer layer undergoes an elastic deformation while the inner pipe undergoes a plastic deformation.
There are two common methods of laying underwater or marine pipelines. The ‘stove piping method’ involves assembling pipe stalks on a marine pipe-laying vessel, and then welding each one as the laying progresses. In the ‘reeled laying method’, the pipeline is assembled onshore and spooled onto a large reel, sometimes also termed a storage reel or drum, and then unwound from the reel as the pipe is being laid. Once offshore, the pipeline is unwound from the reel and is directly available for laying because no welding is required during the offshore operation.
The reeled laying method is faster than the stove piping method, such that it is preferred where possible. However, the reeling process generates bending on the pipeline, which would cause a lined pipe to wrinkle and/or to bend. Thus, there has hitherto been no actual use or commercial application of the reeled lay method for bi-metallic pipes.
WO 2008/072970 A1 discloses a method for laying a pipeline having an inner corrosion proof metallic cladding that is closely fitted with metallic contact to an outer pipe material. In its method, a section of the pipeline is reeled onto a pipe laying drum whilst an overpressure is maintained within the section by means of a pressurised fluid. When the pipeline is motionless, the overpressure is relieved, and a further pipeline section is joined to the first section. A new overpressure is then applied within the sections, and the further section is reeled onto the pipe laying drum.
Whilst this method may assist to avoid deformation when the pipeline sections have no “mechanical movement” (which is defined in WO 2008/072970 A1 as meaning reeling the pipeline onto or unwinding the pipeline from the pipe laying drum), this method requires the overpressuring and pressure-relieving steps every time two pipe sections are joined. The pipe laying drum is described in WO 2008/072970 A1 as typically having installed “many” pre-fabricated sections, creating significant multiplication of the overpressuring and pressure-relieving steps required.